This invention relates to the field of turbofan jet engines, and more particularly to improvements in afterburner or augmentor systems associated therewith.
Axial flow engines of the type concerned are well known and generally comprise an outer housing containing a centrally located fuel burning turbine that produces a central stream of hot "core" gasses and drives an air induction fan in the forward part of the housing. A portion of the air induced by the fan bypasses the turbine as an annular fan stream formed between the turbine and the outer housing so as to surround the core gas stream from the turbine. In afterburner or augmentor operation, additional fuel is added for burning in an afterburner section behind the turbine to produce additional thrust. It is well known that it is advantageous to effect mixing of the two streams during afterburner or augmentor operation for reasons of burning efficiency, noise abatement, infra-red signature reduction, and to permit use of a shorter augmentor structure. The mixing has been accomplished by the use of convoluted mixing chutes or crossover passages, sometimes called "daisy chutes" because of their cross-sectional configuration. In these devices the chuted portions of the fan (cool) and core (hot) streams are circumferentially arranged in alternating segments around the unchuted portion of the core stream. To promote mixing between the alternating segments of fan and core streams, the augmentors have been provided with perforated diffusion panels and with turbulance producing vanes or turbulators that can be actuated from stream aligned positions during normal non-augumented operation to angular positions during augmentor operation. Examples of these alternate segment chuted augmentors or mixers are found in U.S. Pat. Nos. 3,750,402; 4,045,957; and 4,134,260.
Another manner of mixing of the fan and core streams in after burners or augmentors is that resulting from the rotary swirl induced in part by the fan and in some systems by vanes, either fixed or movable, or by angular offsets in flow passages. U.S. Pat. Nos. 3,747,345 and 4,045,947 illustrate swirl mixing in a turbine engine. Rotational swirl in an outer, fan stream having pilot burners or flameholders located therein for ignition of injected fuel is recognized in U.S. Pat. No. 4,203,285 as having a benefit of setting up a radial "g" force that moves hot, lighter gases, from the pilot burner initiated combustion in the fan stream, in inboard directions so as to stabilize afterburner operation.
Because of the circumferentially alternating zones of hot and cool gases surrounding the unchuted portion of the core stream, the concept of rotary swirl induced g forces to improve flame propagation and stability has not been fully utilized in combination with crossover or daisy chute construction. Rather, turbulance producing vanes have been necessary to mix the circumferentially alternating fan and core stream segments as they enter the mixing chamber. These turbulance producing vanes, or turbulators, by their blocking and turbulance producing nature, tend to be less efficient in maintaining parity between entering and leaving velocities than are swirl inducing vanes.